1. Field of the Invention
The present invention relates to a technique preferably applicable to a display module which arranges a touch panel on a display panel.
2. Description of the Related Art
FIG. 6 shows the cross-sectional constitution of a conventional liquid crystal display module which arranges a touch panel on a display panel.
A liquid crystal display panel is constituted by sandwiching a liquid crystal layer not shown in the drawing between a TFT substrate 11 and a color filter substrate 12 (hereinafter, referred to as a CF substrate 12). Further, the TFT substrate 11 is a substrate larger than the CF substrate 12, and a driver chip 13 for controlling driving of the liquid crystal display panel is arranged in a region of the TFT substrate 11 where the TFT substrate 11 and the CF substrate 12 do not overlap each other. Further, an upper polarizer 14 is arranged on an upper side of the CF substrate 12 and, at the same time, a lower polarizer 20 is also arranged on a lower side of the TFT substrate 11. Further, the liquid crystal display module is constituted by arranging a backlight on a lower side of the liquid crystal display panel. Here, numeral 21 indicates a sealing material for sealing liquid crystal between the TFT substrate 11 and the CF substrate 12.
The backlight is constituted of a light source 18 such as an LED arranged on a flexible printed circuit board 15 (hereinafter, referred to as an FPC 15) having one end thereof connected to terminals on the TFT substrate, for example, and a light guide plate 17 for introducing light radiated from the light source 18 to the whole liquid crystal display panel. Here, an optical sheet 22 is arranged between the light guide plate 17 and the liquid crystal display panel. The optical sheet is constituted of, for example, an upper diffusion sheet, an upper prism sheet, a lower prism sheet, a lower diffusion sheet and the like. A reflection sheet 23 is arranged on a lower side of the light guide plate 17 and plays a role of directing light led downwardly from the light guide plate 17 toward a liquid-crystal-display-panel side. The light guide plate 17 has a small thickness except for an incident surface which faces the light source 18 in an opposed manner for satisfying a demand for the reduction of thickness of a liquid crystal display device. The reason that the incident surface has a large thickness is that a size of an LED preferably used as a light source 18 is large and hence, the incident surface of the light guide plate 17 is made large in conformity with the size of the LED. In FIG. 6, numeral 16 indicates a mold frame formed in a frame shape. The liquid crystal display module is configured by arranging the liquid crystal display panel on an upper side of the frame-shaped mold frame 16 and by arranging the backlight on a lower side of the mold frame 16.
By adhering the reflection sheet 23 arranged on a lower side of the light guide plate 17 to the mold frame 16, the light guide plate 17 and the optical sheet 22 are accommodated in the inside of the mold frame 16.
Further, a touch panel 19 is arranged on the liquid crystal display module, and the touch panel 19 performs a function thereof when a user touches the touch panel 19 corresponding to positions of touch keys displayed on the liquid crystal display panel.
The patent document 1 (JP-A-2006-277599) discloses a related art relevant to the constitution of such a touch panel.
FIG. 7 is a view of a liquid crystal display module showing an essential part of the liquid crystal display module in an enlarged manner for explaining a drawback of the conventional constitution shown in FIG. 6. The touch panel 19 is constituted of a film substrate 32 having a lower side thereof covered with a resistance film not shown in the drawing and a glass substrate 31 having an upper side thereof covered with a resistance film not shown in the drawing. The touch panel 19 is configured such that a pushing position is detected when the resistance film of the film substrate 32 and the resistance film of the glass substrate 31 are brought into contact with each other due to pushing of the film substrate 32 with a finger or the like. A plurality of dot spacers 33 is arranged on the glass substrate 31 for ensuring a distance between the film substrate 32 and the glass substrate 31 and for preventing the film substrate 32 and the glass substrate 31 from being adhered to each other after pushing of the touch panel 19.
FIG. 8 shows a state of the touch panel 19 and the CF substrate 12 when the touch panel 19 is strongly pushed with a finger 81 or the like in the constitution of the conventional touch panel 19.
As shown in FIG. 8, when the touch panel 19 is strongly pushed, there exists a possibility that a lower surface of the glass substrate 31 is brought into contact with the upper polarizer 14 arranged on the CF substrate 12. Further, it is also found that once the touch panel 19 and the upper polarizer 14 on the CF substrate 12 are brought into contact with each other as shown in FIG. 8, as a next step, the touch panel 19 and the upper polarizer 14 are adhered to each other thus causing display irregularities or the like. Although the liquid crystal display module is exemplified as a display module in this specification and the liquid crystal display module is preferable as the display module, the present invention is also applicable as a display module of an organic EL panel or of other display panel.